1. Field of the Invention
The present invention relates to a structure for fixing a shielding window of an electronic equipment.
2. Description of the Related Art
As shown in FIG. 5, a cover 51 for covering a front of a frame (not shown) in which an electronic equipment, for example, a communication device is accommodated, essentially includes a bonnet 52 made of a conductive plastic, a metallic shielding plate 53 connected to the reverse side of the bonnet 52, and a shielding window 54 made of transparent plastic and adhered to the bonnet 52 (the shielding plate 53) in such a manner that portions of the shielding window 54 are engaged with rectangular holes (in the case shown in FIG. 5, two rectangular holes are provided) which penetrate through the aforementioned members. Further, shielding gaskets are provided between both sides of the cover 51 and the frame (not shown).
As can be seen from FIG. 7, which is an enlarged sectional view of a portion encircled with a circle C shown in FIG. 6, which is a lateral sectional view of the cover 51, first the surface of the bonnet 52 and that of the shielding plate 53 are entirely coated with an insulating layer (an insulating coated layer) 57, and then the surfaces on the reverse side (the inside) of the bonnet 52 and that of the shielding plate 53 are coated with a carbon coated layer (a conductive layer) 58.
The shielding window 54 is adhered to the reverse side of the bonnet 52 by an annular adhesive layer 59 coated on a small outer circumferential portion (a flange portion) on the side of the mount surface of the shielding window 54, as shown in FIG. 8, and a mesh-shaped conductive member 60 is embedded inside the shielding window 54 in parallel with the front surface (or the rear surface) of the shielding window 54, as shown in FIG. 7.
In order to make the electrical potential of the conductive member 60 equal to that of the cover 51, i.e., in order to ground the conductive member 60, after the shielding window 54 has been adhered thereto, a portion of the conductive member 60 that protrudes slightly from the end surface of the shielding window 54 is cross-linked with the carbon coated layer 58 on the reverse side of the bonnet 52 (the shielding plate 53) by an expensive conductive adhesive 62, as shown in FIGS. 7 and 8.
As can be seen from FIG. 9, which is an enlarged view of a portion encircled with a circle D in FIG. 6, a U-shaped groove portion is provided between an edge portion of the shielding plate 53 and folded inside in such a manner that the folded edge portion is separate from the bonnet 52, and a portion of the bonnet 52 is disposed in parallel to the aforementioned edge portion of the shielding plate 53. A long and slender shielding gasket 55, having a rectangular section, is provided in the U-shaped groove portion.
A large number of ventilation holes 64 are formed in predetermined portions of the bonnet 52 and the shielding plate 53.
In the structure mentioned above, the shielding window 54 and the bonnet 52 (the shielding plate 53) are connected by the annular narrow adhesive layer 59, and accordingly, this is disadvantageous in that a sufficient adhesive strength (joint strength) cannot be stably obtained.
When an amount of adhesive used is small, the adhesion strength becomes lower, and when the amount of adhesive used is increased, to improve the adhesion strength, the adhesive is forced out from a gap and the appearance is deteriorated. Therefore, the adhesion procedure is difficult and troublesome.
In the aforementioned conventional structure, the electric resistance from the shielding window 54 to the frame is high.
Namely, electricity is grounded in the following manner: first electricity flows to the carbon coated surface 58 on the reverse side of the cover from the mesh-shaped conductive member 60 of the shielding window 54 through the conductive adhesive 62; the electricity flows on the carbon coated surface 58, having a relatively high electric resistance to one of the edge portions on the side of the cover; and thereafter, the electricity flows to the shielding plate 53 from the carbon coated surface 58 of the cover edge portion, and flows to the frame ground from the shielding plate 53 through the shielding gasket 55.
As described above, the electrical path on the cover surface is relatively long, and further, the carbon coated surface 58, which constitutes the main portion of the electrical path, has a relatively high electrical resistance, and therefore, a sufficient shielding effect cannot be provided.